/**
 * DB库
 */
var MongoDB = require('mongodb');
var MongoClient = MongoDB.MongoClient;
var ObjectID = MongoDB.ObjectId;
var Config = require('./config.js');

class Db {
  /**
   * 单例
   * 解决多次实例化,实例不共享的问题
   */
  static getInstance () {
    if (!Db.instance) {
      Db.instance = new Db();
    }
    return Db.instance;
  }

  constructor() {
    this.dbClient = ''; /*属性 存放db对象*/
    this.connect(); /*实例化的时候就连接数据库*/
  }

  connect () { /*连接数据库*/
    let _that = this;
    return new Promise((resolve, reject) => {
      if (!_that.dbClient) { /*解决数据库多次连接的问题*/
        MongoClient.connect(Config.dbUrl, (err, client) => {
          if (err) {
            reject(err);
          } else {
            _that.dbClient = client.db(Config.dbName);
            resolve(_that.dbClient);
          }
        })
      } else {
        resolve(_that.dbClient);
      }
    })
  }

  find (collectionName, json) { /*查询数据*/
    return new Promise((resolve, reject) => {
      this.connect().then((db) => {
        var result = db.collection(collectionName).find(json);
        result.toArray((err, docs) => {
          if (err) {
            reject(err);
            return;
          }
          resolve(docs);
        })
      })
    })
  }

  update (collectionName, json1, json2) { /*更新数据*/
    return new Promise((resolve, reject) => {
      this.connect().then((db) => {
        db.collection(collectionName).updateOne(json1, {
          $set: json2
        }, (err, result) => {
          if (err) {
            reject(err);
          } else {
            resolve(result);
          }
        })
      })
    })
  }

  insert (collectionName, json) { /*新增数据*/
    return new Promise((resolve, reject) => {
      this.connect().then((db) => {
        db.collection(collectionName).insertOne(json, function (err, result) {
          if (err) {
            reject(err);
          } else {
            resolve(result);
          }
        })
      })
    })
  }

  remove (collectionName, json) { /*删除数据*/
    return new Promise((resolve, reject) => {
      this.connect().then((db) => {
        db.collection(collectionName).remove(json, function (err, result) {
          if (err) {
            reject(err);
          } else {
            resolve(result);
          }
        })
      })
    })
  }

  getObjectId (id) { /*mongodb里面查询 _id 把字符串转换成对象*/
    return new ObjectID(id);
  }
}

module.exports = Db.getInstance();